As the circuit density increases and the size of the semiconductor decreases, the spacing between the metal wires is consistently reduced, which introduces the problems of electrical migration and RC delay. Usually, a carbon nanotube structure can be used to solve the abovementioned problems. However, it is usually difficult to have a good connection interface and an appropriate contact resistance between a metal wire and a carbon nanotube structure.
R.O.C. patent No. I298520 disclosed a “Method for Electroplating an Interconnection Containing a Carbon Nanotube and Metal Composite Material”, wherein a substrate with an interconnection formed on the surface is electroplated in an electroplating bath containing metal ions and carbon nanotubes to form a conductive wire with carbon nanotubes and metal composite material, whereby the conductive wire has better conductive connection. R.O.C. patent No. 582104 disclosed a “Self-Assembly Nano-Conductive Bump and a Method for Fabricating the Same”, wherein several functional groups are added to two ends of a carbon nanotube, and the carbon nanotube is self-assembled onto a metal pad by powerful complex bonding between the functional groups and the metal pad. Different functional groups can match different metals to create a strong bonding force between the metals and the carbon nanotubes.
U.S. Pat. No. 7,312,531 disclosed a “Semiconductor Device and Fabrication Method Thereof” which proposes a semiconductor device containing wiring layers, wherein a catalyst layer is arranged between a substrate and carbon nanotubes. The catalyst layer is made of cobalt (Co) and M1. M1 is selected from a group consisting of W, P, B, Bi, Ni, and a combination thereof. Further, a top layer made of tantalum (Ta) or tantalum nitride (TaN) is arranged on the carbon nanotubes. The carbon nanotubes are connected to the conductive wires via the top layer to avoid the problem of high resistance. The conventional methods can exempt the interconnection structure from high resistance, disconnection, and pollution or damage to the dielectric layer. However, such a structure increases the number of fabrication steps. Furthermore, the resistance is likely to increase since the substrate interface can easily come in to contact with oxygen during the fabrication process.